Autogenous bone grafts stimulate new bone formation but are prone to resorption. Biomaterials are merely osteoconductive but maintain the volume. So, how about combinations of the two materials?
Prof. Matteo Chiapasco | Italy
Biomaterials, typically xenografts such as bovine bone mineral, are generally used in the form of porous granules. The biomaterial has osteoconductive capabilities and acts as a scaffold, where – thanks to the arrival of blood that contains bone progenitor cells – newly formed bone grows inside and outside the particles.
The main advantage is that biomaterials, if characterized by a very slow resorption rate, will maintain volume. The drawback is that osteoconductive materials are not capable of inducing bone formation themselves. In large reconstructions, and particularly in vertical defects, their efficacy is limited unless combined with autogenous bone.
Autogenous bone: the bone formation promotor
Autogenous bone, on the contrary, both in blocks or particulated in “chips,” has osteoconductive, osteogenic and osteoinductive capabilities. This means that autogenous bone can act as a scaffold while at the same time promoting new bone formation by itself. The reason is that autogenous bone contains bone morphogenetic proteins, and sometimes live cells, which can activate new bone formation.1-3
Autogenous bone is still considered the “gold standard” for bone augmentation to which all biomaterials should be compared. Also, it can be used successfully for cases requiring large vertical reconstructions. The main drawback, however, is postoperative morbidity due to the necessity for bone harvest from intra-oral or extraoral sites (extraoral sites, such as the iliac crest or the calvarium, are used only when large amounts of bone are needed). In addition, autogenous bone volume can be lost due to resorption and remodeling in the long-term.
Combinations
Clinicians can minimize the disadvantages and maximize the advantages of both materials by combining autogenous bone particles or blocks with their osteoinductive and osteogenic capabilities, and biomaterials with their osteoconductive capabilities, along with their capacity for maintaining volume over time, thus minimizing the loss of initial bone gains.
Biomaterials, in the form of porous granules, can be effectively used without autogenous bone in the following cases:
Autogenous bone blocks can be used in any inlay and, in particular, onlay grafting procedure for the correction of both horizontal or vertical defects, from single tooth gaps to fully edentulous, deficient alveolar ridges.4 In such cases, bone blocks can be covered with a layer of slowly resorbing biomaterials and a collagen membrane to reduce the risk of graft resorption over time.5
Finally, particulated autogenous bone and biomaterials in a 1:1 ratio, approximately, can be safely used in the following indications:
Loss of teeth 45 and 46 with horizontal atrophy of the residual ridge.
CBCT picture of the region shows reduced bone volume.
The bone defect after flap exposure.
Correction of the bone defect with two autogenous bone blocks harvested from the mandibular ramus.
Filling of every void between the grafts and the recipient bed with autogenous bone chips mixed in a 1:1 ratio with bovine bone mineral.
Coverage of the graft with a resorbable collagen membrane.
Water-tight closure of the flaps to guarantee primary healing of the surgical wound.
The radiographic picture shows that an adequate bone volume has been obtained.
Final prosthetic results after the insertion of two endosseous implants in the reconstructed area.
Prof. Matteo Chiapasco | Italy
Department of Biomedical, Surgical and Dental Sciences
University of Milan
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